When a power transformer is operated, since the change of an incoming voltage or the change of a load will cause the change of an output voltage, the secondary output voltage can be changed by changing the number of turns of primary windings of the power transformer, thereby achieving a purpose of regulating or stabilizing the voltage. A purpose of changing the output voltage can be achieved by using a tap switch to change the number of turns of coils. On-load voltage regulation of the transformer is to change the number of turns of the primary windings of the transformer through an on-load regulation tap switch when the transformer is not powered off and is under a normal working condition, and this is a task to be completed by the on-load voltage regulation (tapping) switch. The on-load tap switch mainly consists of a selection switch, a changeover switch and a rotating mechanism; and in the nearly 100 years of development history of the on-load tap switch, the electrical and mechanical properties of the on-load tap switch are greatly improved, but the basic principle and structure are essentially not changed. Failure of the on-load tap switch mainly includes two aspects, i.e. the electrical property and the mechanical property: the electrical property mainly refers to a contact resistance of a contact, and when the contact resistance of the contact is increased, the contact may be over-heated and even burnt down. The mechanical property refers to a coordination between an action sequence and time for the selection switch, the changeover switch and other components in the operation process of the on-load tap switch (OLTC), as well as clamping, insufficient contact changeover and the like in the switching process.
When the tap switch acts, the sudden change of a current in a primary coil of the transformer may be caused, which may generate a high counter self-induction electromotive force to generate an electric arc at the contact, resulting in the burning of the contact; a vacuum-type switch is used to substitute an oil-immersion switch, so that the reliability of the contact can be improved, but the cost is greatly increased; and on the other hand, the vacuum-type switch cannot solve the problem of the sudden change of the current in the primary coil, and the suddenly-changed current may generate residual flux which is easy to cause the overload and burning of the transformer when the transformer is fully-loaded.